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Abstract

First order approximations of the rates of emission of isoprene and α-pinene are made for the region around London. Isoprene is found to be the dominant biogenic non-methane hydrocarbon species by mass in the region. Chemical degradation schemes for isoprene and α-pinene are added to an existing urban plume model which has previously been applied to London. The influence of each hydrocarbon is investigated by comparing model runs which include biogenic chemistry to a base case scenario. Oveerall, the effect is small: ozone levels in the plume are increased by the addition of the new schemes by up to 88 ppb. A model run with biogenic hydrocarbon and NOx emissions only demonstrates the VOC-limited behaviour of the urbans plume. Conversely, removall of anthropenic VOC emissions from the rural/suburban model results in a decrease of only 5 ppb in ozone production over one day. The reason for this difference in behaviour is the different NMHC/NOx ratios within and outside the urban plume. The inclusion of biogenic NMHC chemistry in the model results in a negligible change to the calculated ‘urban ozone effect’ defined as as the difference between ozone concentrations within and outsside of the plume. Substantial enhancement to present biogenic NMHC database are required if our understanding of urban plume chemistry is to be made more accurate.

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... For example, 126 different species of mature trees have been recorded in London (Treeconomics 2015) and 170 in Beijing (Yang et al. 2005). bVOCs take part in chemical reactions in the atmosphere that can lead to the formation of ozone (MacKenzie et al. 1991;Chameides et al. 1988;Atkinson and Arey 2003;Donovan et al. 2005;Calfapietra et al. 2013) and organic aerosol particles (Carlton et al. 2009;Hallquist et al. 2009;Mentel et al. 2009;Wyche et al. 2014), both of which are important secondary air pollutants. Since it takes several hours before these chemical reactions generate high pollutant concentrations of ozone or particles, the precise location of bVOC-emitting GI within the urban canopy is not important. ...
... bVOC emissions from a typical urban tree population contribute on the order of 10% to ozone concentrations within and downwind of large city-regions (MacKenzie et al. 1991;Chameides et al. 1988;Donovan et al. 2005;Calfapietra et al. 2013). Unfortunately, there is no easy way to reliably predict whether or not a given tree species emits a particular bVOC, or at what specific rate. ...
Article
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As evidence for the devastating impacts of air pollution on human health continues to increase, improving urban air quality has become one of the most pressing tasks facing policy makers world-wide. Increasingly, and very often on the basis of conflicting and/or weak evidence, the introduction of green infrastructure (GI) is seen as a win–win solution to urban air pollution, reducing ground-level concentrations without imposing restrictions on traffic and other polluting activities. The impact of GI on air quality is highly context dependent, with models suggesting that GI can improve urban air quality in some situations, but be ineffective or even detrimental in others. Here we set out a novel conceptual framework explaining how and where GI can improve air quality, and offer six specific policy interventions, underpinned by research, that will always allow GI to improve air quality. We call GI with unambiguous benefits for air quality GI4AQ. However, GI4AQ will always be a third-order option for mitigating air pollution, after reducing emissions and extending the distance between sources and receptors.
... Even given the reactivity of many BVOCs the formation of ozone or generation of secondary aerosols is not instantaneous, and the majority of effects from additional BVOC emissions would occur some distance downwind, with regional increases in air pollution rather than substantial BVOC-induced changes in urban centres themselves (see for example Mackenzie et al. 1991). These spatial effects of urban emissions of BVOCs are illustrated by Nowak et al. (2000), who modelled that changing tree coverage in cities (from 20 to 40%) led to modest decreases in urban ozone (~1 ppb) and increases (0.26 ppb) in the wider regional domain. ...
... These studies are based on inventories of anthropogenic and biogenic emissions and are driven by local climate. Sensitivity studies for the urban plume in London, where photochemistry is strongly VOC limited, showed a potentially large effect of BVOCs on ozone formation MacKenzie et al. 1991). More specifically, calculations for Paris, France, yielded a BVOC contribution of about 18-30 % (Solmon et al. 2004). ...
Technical Report
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Volatile organic hydrocarbons, which are released to the atmosphere by plants (biogenic VOC, BVOC), have large influence on atmospheric chemistry and thus air quality. They are beside nitrogen oxides and anthropogenic VOC eminent precursors for tropospheric ozone and may also foster the creation of aerosols. This literature review summarizes the current knowledge about functions, drivers and impacts of BVOC and analyses which environmental factors influence their formation.
... Real et al., 2007Real et al., , 2008, running a "background" box prior to running the box of interest (e.g. MacKenzie et al., 1991), or using evolving fields from a Eulerian model to define the background. Stochastic mixing has also been applied in the Lagrangian framework (Pisso et al., 2009). ...
Article
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A Lagrangian model of photochemistry and mixing is described (CiTTyCAT, stemming from the Cambridge Tropospheric Trajectory model of Chemistry And Transport), which is suitable for transport and chemistry studies throughout the troposphere. Over the last five years, the model has been developed in parallel at several different institutions and here those developments have been incorporated into one "community" model and documented for the first time. The key photochemical developments include a new scheme for biogenic volatile organic compounds and updated emissions schemes. The key physical development is to evolve composition following an ensemble of trajectories within neighbouring air-masses, including a simple scheme for mixing between them via an evolving "background profile", both within the boundary layer and free troposphere. The model runs along trajectories pre-calculated using winds and temperature from meteorological analyses. In addition, boundary layer height and precipitation rates, output from the analysis model, are interpolated to trajectory points and used as inputs to the mixing and wet deposition schemes. The model is most suitable in regimes when the effects of small-scale turbulent mixing are slow relative to advection by the resolved winds so that coherent air-masses form with distinct composition and strong gradients between them. Such air-masses can persist for many days while stretching, folding and thinning. Lagrangian models offer a useful framework for picking apart the processes of air-mass evolution over inter-continental distances, without being hindered by the numerical diffusion inherent to global Eulerian models. The model, including different box and trajectory modes, is described and some output for each of the modes is presented for evaluation. The model is available for download from a Subversion-controlled repository by contacting the corresponding authors.
... The overall assessment of vegetation (not considered here), is a complex interplay between wind dynamics, deposition and chemistry, including biogenic volatile organic compounds (BVOCs). These can lead on to new particle formation as BVOCs play an important role in the atmospheric oxidation cycles (MacKenzie et al. (1991), Donovan et al. (2005)). Vegetation has been shown to be both beneficial and harmful. ...
Article
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This paper focuses on the effectiveness of trees at dispersing road traffic emissions on a city scale. CFD simulations of air-pollutant concentrations were performed using the OpenFOAM software platform using the k-. ε model. Results were validated against the CODASC wind tunnel database before being applied to a LIDAR database of buildings and trees representing the City of Leicester (UK). Most other CFD models in the literature typically use idealised buildings to model wind flow and pollution dispersion. However, the methodology used in this study uses real buildings and trees data from LIDAR to reconstruct a 3D representation of Leicester City Centre. It focuses on a 2 × 2 km area which is on a scale larger than those usually used in other CFD studies. Furthermore, the primary focus of this study is on the interaction of trees with wind flow dynamics. It was found that in effect, trees have a regionally beneficial impact on road traffic emissions by increasing turbulence and reducing ambient concentrations of road traffic emissions by 7% at pedestrian height on average. This was an important result given that previous studies generally concluded that trees trapped pollution by obstructing wind flow in street canyons. Therefore, this study is novel both in its methodology and subsequent results, highlighting the importance of combining local and regional scale models for assessing the impact of trees in urban planning.
... The urban classification and application of published tree data for the UKWM area has produced the first detailed estimate of BVOC emissions from this metropolitan region. MacKenzie et al. (1991) used a crude land-use categorization (deciduous forest, coniferous forest, scrubland, and grassland), and the ratio of high forest in urban and rural Southeast England, to calculate BVOC emission potentials for Greater London. While these workers' BVOC (isoprene) emission estimates are similar (per unit area) to our estimates for the UKWM (e.g., 1087 g·km Ϫ2 ·h Ϫ1 for Greater London, cf. ...
Article
Biogenic emissions of the volatile organic compounds isoprene and monoterpenes (BVOCs) can contribute to tropospheric ozone and secondary particle formation and have indirect effects on climate change. While there are few studies of BVOC emissions from European towns and cities, several studies in North America indicate that the urban tree canopy may be a significant source of BVOC compounds, contributing to ozone and particle formation in the urban air-shed. Here, BVOC emissions from the U.K. West Midlands (UKWM) metropolitan area were estimated and compared with anthropogenic VOC emission estimates, and with BVOC emission estimates for other urban and U.K. regions. Monoterpene and isoprene emission potential estimates for the UKWM urban land-use classes spanned as much as two orders of magnitude, from 17-104 g·km-2·h-1 and from 42-1570 g·km -2·h-1, respectively. Isoprene emission potential estimates for the UKWM urban land classes (42-530 g·km -2·h-1) were of the same order of magnitude as isoprene emission measurements for U.K. gorse heathland in early summer (43 g·km-2·h-1)> and up to approximately one order of magnitude lower than those measured from U.K. Sitka spruce forests in summer (658-6760 g·km-2·h-1). In the UKWM, the land class average of ΣBVOC emission estimates (∼75-165 kg·km-2·yr-1) were approximately two orders of magnitude lower than anthropogenic VOC emission estimates for the same area (70000 kg·km-2·yr-1)-Biogenic isoprene emission estimates from at least two of the UKWM urban land-use classes were equivalent to, or greater than, estimates of anthropogenic isoprene emissions. The extrapolation methodologies are critically discussed in the context of their uncertainties, and in the context of their generic potential.
... Volatile organic compounds (VOCs) are important indoor air pollutants because they are ubiquitous and numerous. Among the 189 chemicals that have been identified as hazardous air pollutants by Clean Air Act Amendments, nearly 100 of them are VOCs [1]. They can be irritant to people and there are indications that VOCs may be a cause of the sick building syndrome [2]. ...
Article
Full-text available
Although volatile organic compounds (VOCs) are major indoor air pollutants and ones which may affect human health it is rare to find a study about their types and distribution pattern in a university. To remedy this large-scale sampling of VOCs was conducted at different indoor environments on a university campus in Hong Kong when the HVAC system was turned on. The 54 sites selected for sampling included classrooms, offices, dining and kitchen area of canteens, workshops, laboratories and a library. All the buildings were served with mechanical ventilation and an air conditioning (MVAC) system. Samples were analysed by the USEPA's TO-14 method. VOCs discovered were divided arbitrarily into three categories: fluorinated compounds, non-aromatic chlorinated compounds and aromatic compounds. Among the VOCs detected by the TO-14 method, toluene and benzene were the most common compounds present on the campus and were present in all the samples taken. The main source for those two VOCs was ingress from outdoors.
... Real et al., 2007Real et al., , 2008, running a "background" box prior to running the box of interest (e.g. MacKenzie et al., 1991), or using evolving fields from a Eulerian model to define the background. Stochastic mixing has also been applied in the Lagrangian framework (Pisso et al., 2009). ...
Article
Full-text available
A Lagrangian model of photochemistry and mixing is described (CiTTyCAT, stemming from the Cambridge Tropospheric Trajectory model of Chemistry And Transport), which is suitable for transport and chemistry studies throughout the troposphere. Over the last five years, the model has been developed in parallel at several different institutions and here those developments have been incorporated into one "community" model and documented for the first time. The key photochemical developments include a new scheme for biogenic volatile organic compounds and updated emissions schemes. The key physical development is to evolve composition following an ensemble of trajectories within neighbouring air-masses, including a simple scheme for mixing between them via an evolving "background profile", both within the boundary layer and free troposphere. The model runs along trajectories pre-calculated using winds and temperature from meteorological analyses. In addition, boundary layer height and precipitation rates, output from the analysis model, are interpolated to trajectory points and used as inputs to the mixing and wet deposition schemes. The model is most suitable in regimes when the effects of small-scale turbulent mixing are slow relative to advection by the resolved winds so that coherent air-masses form with distinct composition and strong gradients between them. Such air-masses can persist for many days while stretching, folding and thinning. Lagrangian models offer a useful framework for picking apart the processes of air-mass evolution over inter-continental distances, without being hindered by the numerical diffusion inherent to global Eulerian models. The model, including different box and trajectory modes, is described and some output for each of the modes is presented for evaluation. The model is available for download from a Subversion-controlled repository by contacting the corresponding authors.
... In accordance with the 1990 Clean Air Act Amendments [Section 182 (C) (1)], the US EPA developed rules for the initiation of Photochemical Assessment Monitoring Stations (PAMS) located in ozone non-attainment areas for measuring a list of 55 nonmethane hydrocarbons (NMHCs) (Robert MacKenzie et al., 1991). These NMHCs encompass an important portion of ambient volatile organic compounds (VOCs), in terms of composition and abundance (Parrish et al., 1998). ...
Article
Continuous monitoring of ambient non-methane hydrocarbons (NMHCs) by automated gas chromatographs equipped with flame ionization detection (termed in-situ GC/FID) with hourly data resolution was instated in ozone non-attainment areas throughout Taiwan. Performance of these on-site in-situ GCs was validated by manual flask sampling, as well as by in-lab gas chromatography/mass spectrometry (GC/MS) analysis. More than 50 VOCs from C2 to C11 were analyzed by both methods. Ninety flask samples were collected in series near an in-situ GC monitoring station in order to closely compare with the in-situ measurements. Both time-series and scatter plots from the two methods are displayed and discussed. It was found that over-simplified, un-humidified single-point calibration leading to surface loss was responsible for the bias in the in-situ method, resulting in greater error in accuracy as VOC volatility decreased. Although this over-estimate of the concentrations was found across all target VOCs, both methods were able to consistently capture the variability of ambient VOCs, with R2 values greater than 0.9 for most of the major VOCs.
... Firstly, VOCs are ubiquitous and numerous in the environment, workplace, and consumer products (Brown et al. 1994; Wolkoff and Nielsen 2001). Among the 189 chemicals which have been identified as hazardous air pollutants by Clean Air Act Amendments, nearly 100 of them are VOCs (MacKenzie et al. 1991). Therefore, humans can be easily exposed to VOCs through skin contact, breathing, and eating. ...
Article
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This study explores a bibliometric approach to quantitatively assessing current research trends on volatile organic compounds, by using the related literature in the Science Citation Index (SCI) database from 1992 to 2007. The articles acquired from such literature were concentrated on the general analysis by scientific output, the research performances by countries, institutes, and collaborations, and the research trends by the frequency of author keywords, words in title, words in abstract, and keywords plus. Over the past years, there had been a notable growth trend in publication outputs, along with more participation and collaboration of countries and institutes. Research collaborative papers had shifted from the national inter-institutional to the international collaboration. Benzene, toluene, and formaldehyde were the three kinds of VOCs concerned mostly. Detection and removing, especially by adsorption and oxidation, of VOCs were to be the orientation of all VOCs research in the next few years.
... BVOC emissions were introduced into European regional air quality research models in the late 1980s (e.g. MacKenzie et al., 1991) and later into regulatory simulations (Simpson, 1995). ...
Article
The coupling between climate change and atmospheric composition results from the basic structure of the Earth atmosphere climate system, and the fundamental processes within it. The composition of the atmosphere is determined by natural and human-related emissions, and the energy that flows into, out of, and within the atmosphere. Atmospheric composition influences climate by regulating the radiation budget. Potentially significant contributions to the climate impact are provided by compounds such as CO2, CH4, O3, particles, and cirrus clouds. For the chemically active gases, processes in the atmosphere are important, with large spatial and temporal variations. The climate-chemistry interactions are therefore characterized by significant regional differences with regions such as South East Asia being a future key region due to significant increases in energy use and pollution emission. Likewise, ship and air traffic represent important sectors because of significant increases in emissions in recent years. The relative contributions to the emissions from various sectors are expected to change significantly over the next few decades due to differences in mitigation options and costs.
... As a result of the atmospheric reactions of these products, nitrogen oxide (NO) is converted to ni.trogen dioxide (NO2); this conversion is an important precursor reaction to ozone formation. Much research has been undertaken in an effort to better understand and quantify this effect (Lloyd et al., 1983; Chameides et al., 1988 Chameides et al., ,1992 Lopez et al., 1989; Atherton and Penner, 1990; MacKenzie et al., 1991; McKeen et al., 1991; Linet al., 1992). In addition to efforts to accurately determine anthropogenic emissions of NOx (NOx = NO + NO2) and VOCs, accurate estimates of BVOC fluxes are needed to fully understand the factors contributing to tropospheric ozone formation in both urban and remote areas (Roselle et al., 1991; Roselle 1994). ...
Article
Vegetation composition and biomass were surveyed for three specific sites in Atlanta, GA; near Rhinelander, WI; and near Hayden, CO. At each research site emissions of biogenic volatile organic compounds (BVOCs) from the dominant vegetation species were sampled by enclosing branches in bag enclosure systems and sampling the equilibrium head space onto multi-stage solid adsorbent cartridges. Analysis was performed using a thermal desorption technique with gas chromatography (GC) separation and mass spectrometry (MS) detection. Identification of BVOCs covering the GC retention index range (stationary phase DB-1) from approximately 400 to 1400 was achieved (volatilities C4-C14).
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Biogenic emissions have been the driving force in forming the global atmosphere during earth history. The current concentration of the major gases in the atmosphere, N2 and O2, is the result of photosynthesis and microbial activity. Important characteristics of the atmosphere, such as the radiation and energy balance, the concentration of oxidants in the troposphere, and the absorption of UV radiation in the stratosphere, arc controlled by biogenically emitted compounds like O2, CO2, H2O, CH4, and N2O, in a complex, interconnected system that has been portrayed by Lovelock (1979) as the Gaia system. Today, we have become aware of the potential effects of anthropogenic emissions on the chemical and physical characteristics of the atmosphere and reciprocal effects on the biosphere. The above characteristics of the atmosphere are part of the so-called global change phenomenon, including such global concerns as greenhouse warming or the polar ozone hole. Understanding such symptoms of a changing global environment will require understanding of the underlying natural processes.
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Air quality transcends all scales with in the atmosphere from the local to the global with handovers and feedbacks at each scale interaction. Air quality has manifold effects on health, ecosystems, heritage and climate. In this review the state of scientific understanding in relation to global and regional air quality is outlined. The review discusses air quality, in terms of emissions, processing and transport of trace gases and aerosols. New insights into the characterization of both natural and anthropogenic emissions are reviewed looking at both natural (e.g. dust and lightning) as well as plant emissions. Trends in anthropogenic emissions both by region and globally are discussed as well as biomass burning emissions. In terms of chemical processing the major air quality elements of ozone, non-methane hydrocarbons, nitrogen oxides and aerosols are covered. A number of topics are presented as a way of integrating the process view into the atmospheric context; these include the atmospheric oxidation efficiency, halogen and HOx chemistry, night time chemistry, tropical chemistry, heat waves, megacities, biomass burning and the regional hot spot of the Mediterranean. New findings with respect to the transport of pollutants across the scales are discussed, in particular the move to quantify the impact of long-range transport on regional air quality. Gaps and research questions that remain intractable are identified. The review concludes with a focus of research and policy questions for the coming decade. In particular, the policy challenges for concerted air quality and climate change policy (co-benefit) are discussed. doi:10.1016/j.atmosenv.2009.08.021.
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The role of urban plumes in the exposure of suburban/rural areas to pollution by ozone is discussed, and literature on direct measurement of ozone within plumes reviewed. There is a virtual absence of reports of ozone destruction within a NOx-rich urban plume and reasons are given for this gap in the current published data. These negative ozone increments are important because the particular air quality problems encountered downwind of a city will depend on its character as a source or sink of ozone. Simple plume reconstruction methods are used to verify and extend data from measurements in the London plume. There is an optimum time for air-parcel release with respect to increased plume ozone, and a change in the typical diurnal variation of ground-level ozone concentrations when the receptor site is situated within an urban plume. On a surface constructed from air parcel emission times and times travelled downwind of London, a major peak in plume ozone increment is observed 6–8 h downwind of a post rush-hour release in the urban centre. A secondary maximum in the surface is also apparent for air parcels 2–3 h after release in the early afternoon. These are not the emission and travel times usually adopted in modelling studies of the urban plume from London. Sites in the urban plume are also found to have a statistically different diurnal variation compared to rural/suburban sites which are not influenced by the plume. This is due to the titration of ozone mixing into the plume from aloft by plume NO.
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The spatial pattern of summertime ozone concentrations across the British Isles has been revealed using a simple long-range transport model (ELMO). The model describes the chemical development of air parcels reaching an array of 3064 arrival points after 4 days of travel across Europe during typical summertime photochemical episodic conditions. Model results have been compared against observations and the model responses to VOC and NOx controls against established indicator ratios. The model has been used to assess the likely impacts of policy commitments under the Gothenburg Protocol to the United Nations Convention on Long-Range Transboundary Air Pollution and other policy instruments.
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The potential emission of the reactive non-methane hydrocarbons (NMHC), isoprene and the monoterpenes, have been qualitatively assessed for the most abundant tree, crop and plant species in the U.K. Most coniferous trees, some deciduous trees, and a few herbaceous, grass and crop species emit one or more of these compounds. Factors likely to influence NMHC emissions from vegetation are reviewed as are current literature estimates of their emission rates for the U.K. These estimates are considered to be very uncertain at the present time, but may lie in the range 50–100 kt yr−1, with emissions of monoterpenes dominating those of isoprene. Assessment is made of the likely cause of uncertainty.
Article
The ability of a new graphitized carbon black adsorbent (Carbograph 5) to retain volatile organic compounds (VOCs) in air has been investigated through laboratory experiments performed by frontal chromatography. An artificial mixture containing 19 different compounds from C1 to C7 at levels of 50 ppb (v/v) each was used as eluent. The amounts of VOCs retained by Carbograph 5 were determined by high-resolution GC–flame ionization detection after thermal desorption at 250°C. The retention features of this adsorbent were compared with those provided by Carbograph 1 and Carbograph 2, two graphitic carbons equivalent in specific surface area and adsorption properties to Carbopack B and Carbopack C, respectively. It was found that Carbograph 5 exhibits safe sampling volumes of VOCs much higher than those of Carbograph 1 and is the only hydrophobic material providing performances comparable to those of some molecular sieve adsorbents. Results obtained indicate that Carbograph 5 can be used alone or in combination with other materials. When combined with lighter adsorbents, it allows the quantitative collection of polar and non-polar VOCs with carbon number higher than 3 in air volumes larger than 5 l at any relative humidity. In combination with stronger carbon molecular sieve adsorbents, it makes possible the quantitative collection of components with volatilities ranging from C2 to C7 in small samples.
Article
Monoterpene concentrations have been measured in four open-top chambers with Norway spruce (Picea abies L. Karst). In half of the chambers used in this study the trees had been exposed to charcoal-filtered air during five summer periods, in the others they had been exposed to ambient air with additional ozone during the same periods. Measurements were performed during two periods, one in September–October during the fifth treatment, and the other in April–May, just before the harvest. Higher terpene concentrations were usually found in the chambers with filtered air, but this difference disappeared when the concentrations were adjusted according to differences in biomass. Consequently, these results do not indicate that ozone stress, at the levels tested, would lead to an increased release of terpenes. The estimate of the emission rate of α-pinene, obtained using the results from the spring measurements, are in good agreement with the findings in other, comparable investigations.
Article
A fully automated sampling/injection system for the gas chromatographic-mass spectrometric (GC-MS) analysis of volatile organic compounds at tropospheric background levels was developed. Organic trace gases from air samples up to 100 l were trapped in temperature-controlled solid-adsorbent traps. The instrument utilized a one stage sampling/desorption inlet system designed as a closed device that did not require any replumbing steps between sampling and analysis. For analysis, the adsorbent trap was thermally desorbed and backflushed onto the chromatographic column where organic trace gases were directly cryofocused. Adsorbents tested were Carbotrap, Carbotrap C, Carbosieve S III, Tenax TA, Tenax GR and multistage combinations of these adsorbents. Interferences from blanks and adsorbent artifacts were minimized by backflushing the adsorbent trap, switching valve and transfer line between sampling sequences at temperatures above the levels used during trapping and sample transfer. The high sample volumes that could be concentrated and the low background levels allowed structural identification in GC-MS (electron impact ionization scan mode) at minimum levels of ca. 100 pg per peak (ca. 10-(12) mol) equivalent to atmospheric concentrations at the lower parts per trillion (v/v) level. The volatility range of organic compounds that could be identified was approximately from pentane to pentadecane. The system was completely computer controlled and could be operated continuously and unattended around the clock for in situ analysis. The instrument was successfully deployed at the Mauna Loa Observatory, Hawaii, USA in July and August 1992.
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Several biogenic volatile organic compound (VOC) emission algorithms have been used, together with meteorological data from the EMEP MSC-W ozone model, to generate estimates of the emissions of isoprene from European forests and agricultural crops over several summer periods. The most up-to-date estimate combines the recently updated isoprene emission factors from the United States with available knowledge of European tree species and emission factors. In some cases these European emission factors are significantly different from their U.S. equivalents because of differences in the tree species represented within a forest classification, especially with regard to spruce genera and Mediterranean oak genera. The new estimates have resulted in an approximate factor of 2-3 increase in isoprene emissions from northern Europe but a factor of 2 decrease in isoprene estimates for southern Europe. Overall, European isoprene emissions are estimated to be about 4000 kt C yr(-1), approximately 50-100% greater than previous estimates. Preliminary estimates are also made of the emissions of the so-called OVOC (other VOC) from forests and of soil NOx emissions. All of these estimates of biogenic emissions are subject to considerable uncertainty, not least because of a lack of knowledge of the species coverage in most European countries and of the appropriate emission factors which should be applied. Factors of 5-10 uncertainty are not unlikely for episodic ozone calculations. The implications of these uncertainties for the results of control strategy evaluations for rural ozone in Europe are assessed in a companion paper.
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Air quality transcends all scales with in the atmosphere from the local to the global with handovers and feedbacks at each scale interaction. Air quality has manifold effects on health, ecosystems heritage and, climate. In this review the state of scientific understanding in relation to global and regional air quality is outlined. The review discusses air quality, in terms of emissions, processing and transport of trace gases and aerosols. New insights into the characterization of both natural and anthropogenic emissions are reviewed looking at both natural (e.g. dust and lightning) as well as plant emissions. Trends in anthropogenic emissions both by region and globally are discussed as well as biomass burning emissions. In terms of chemical processing the major air quality elements of ozone, non-methane hydrocarbons, nitrogen oxides and aerosols are covered. A number of topics are presented as a way of integrating the process view into the atmospheric context; these include the atmospheric oxidation efficiency, halogen and HOx chemistry, nighttime chemistry, tropical chemistry, heat waves, megacities, biomass burning and the regional hot spot of the Mediterranean. New findings with respect to the transport of pollutants across the scales are discussed, in particular the move to quantify the impact of long-range transport on regional air quality. Gaps and research questions that remain intractable are identified. The review concludes with a focus of research and policy questions for the coming decade. In particular, the policy challenges for concerted air quality and climate change policy (co-benefit) are discussed. (C) 2009 Elsevier Ltd. All rights reserved.
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Biogenic volatile organic compounds (BVOCs) and their role in atmospheric oxidant formation were investigated at a forest site near Oak Ridge, Tennessee, as part of the Nashville Southern Oxidants Study (SOS) in July 1995. Of 98 VOCs detected, a major fraction were anthropogenic VOCs such as chlorofluorocarbons (CFCs), alkanes, alkenes and aromatic compounds. Isoprene was the dominant BVOC during daytime. Primary products from BVOC oxidation were methylvinylketone, methacrolein and 3-methylfuran Other compounds studied include the BVOCs cr-pinene, camphene, beta-pinene, p-cymene, limonene and cis-3-hexenyl acetate and a series of light alkanes, aromatic hydrocarbons and seven of the CFCs. The correlation of meteorological parameters, with the mixing ratios of these different compounds, reveals information on atmospheric oxidation processes and transport. Long-lived VOCs show very steady mixing ratio time series. Regionally and anthropogenically emitted VOCs display distinct diurnal cycles with a strong mixing ratio decrease in the morning from the breakup of the nocturnal boundary layer. Nighttime mixing ratio increases of CFCs and anthropogenic VOCs are suspected to derive from emissions within the Knoxville urban area into the shallow nocturnal boundary layer. In contrast, the time series of BVOCs and their oxidation products are determined by a combination of emission control, atmospheric oxidation and deposition, and boundary layer dynamics. Mixing ratio time series data for monoterpenes and cis-3-hexenyl acetate suggest a temporarily emission rate increase during and after heavy rain events. The isoprene oxidation products demonstrate differences in the oxidation pathways during night and day and in their dry and wet deposition rates.
Article
Vegetation provides a major source of reactive carbon entering the atmosphere. These compounds play an important role in (1) shaping global tropospheric chemistry, (2) regional photochemical oxidant formation, (3) balancing the global carbon cycle, and (4) production of organic acids which contribute to acidic deposition in rural areas. Present estimates place the total annual global emission of these compounds between approximately 500 and 825 Tg yr-1. The volatile olefinic compounds, such as isoprene and the monoterpenes, are thought to constitute the bulk of these emissions. However, it is becoming increasingly clear that a variety of partially oxidized hydrocarbons, principally alcohols, are also emitted. The available information concerning the terrestrial vegetation as sources of volatile organic compounds is reviewed. The biochemical processes associated with these emissions of the compounds and the atmospheric chemistry of the emitted compounds are discussed.
Article
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998. Includes bibliographical references (p. 169-180). by John J. Graham, Jr. Ph.D.
Article
An automated gas chromatographic system was constructed to easily adapt either the cryogenic trap or chemical sorbent trap for preconcentrating ambient levels of volatile organic compounds. Remarkable similarity in chromatograms from C3 to C10 was found between these two enrichment methods, except that the sorbent trap did not quantitatively trap the C2-hydrocarbons. In contrast to cryogenic trapping, the chromatographic conditions for more volatile compounds were substantially improved using the sorbent trap. Water interference on the porous-layer open tubular column was also better managed using the sorbent trap for the continuous analysis of humid room air. The similarity in peak profiles between the GC-flame ionization detection (FID) and a commercial GC-MS system, regardless of concentration levels, facilitated compound identification on the FID chromatograms based on a field mission involving analysis of 106 air samples.
Article
An automated gas chromatographic (auto-GC) system aiming at performing unattended hourly measurement of ozone precursors was developed in the laboratory. To encompass volatile organic compounds (VOCs) of a wide range of volatility within each analysis, the system uses dual-traps and dual-columns to simultaneously analyze both low and high-boiling compounds with each injection. Since sorbents with sufficient retention of C2 compounds at room temperature, namely ethane, ethene, and ethyne are not yet available, cooling with a thermoelectrical device was built around the low-boiling trap to facilitate quantitative enrichment of C2 compounds. The effectiveness of using micro-trap with low dead volume plumbing was manifested in reducing peak width and increasing peak height for particularly the lower-boiling compounds. The increase in sensitivity allowed sufficient detector response with a small amount of air sample, e.g. 200 ml in our routine operation, which in term eliminate the need for remove water prior to sampling trapping. The performance and applicability of this laboratory-built auto-GC system was validated by comparison with a commercial analog, i.e. the ATD-400 system made by Perkin-Elmer, in the field sharing a common air intake. During more than 3 weeks of synchronized monitoring of ambient volatile organic compounds both systems showed highly consistent results on almost every monitored compound, clearly demonstrating the robustness of this self-built system.
Article
Live-oak plants (Quercus virginiana Mill.) were subjected to various levels of CO2, water stress or photosynthetic photon flux density to test the hypothesis that isoprene biosynthesis occurred only under conditions of restricted CO2 availability. Isoprene emission increases as the ambient CO2 concentration decreased, independent of the amount of time that plants had photosynthesized at ambient CO2 levels. When plants were water-stressed over a 4-d period photosynthesis and leaf conductance decreased 98 and 94%, respectively, while isoprene emissions remained constant. Significant isoprene emissions occurred when plants were saturated with CO2, i.e., below the light compensation level for net photosynthesis (100 μmol m(-2) s(-1)). Isoprene emission rates increased with photosynthetic photon flux density and at 25 and 50 μmol m(-2) s(-1) were 7 and 18 times greater than emissions in the dark. These data indicate that isoprene is a normal plant metabolite and not - as has been suggested - formed exclusively in response to restricted CO2 or various stresses.
The observed ranges in nonmethane organic compound (NMOC) concentrations, NMOC composition and nitrogen oxides (NOX) concentrations have been evaluated for urban and nonurban areas at ground level and aloft of the contiguous United States. The ranges in NMOC to NOX ratios also are considered. The NMOC composition consistently shifts towards less reactive compounds, especially the alkanes, in air parcels over nonurban areas compared to the NMOC composition near ground level within urban areas. The values for the NMOC to NOX ratios, 1.2 to 4.2, in air aloft over nonurban areas are lower than in air at ground level urban sites, ≥8, and much lower than in air at ground level nonurban sites, ≥20.The layers of air aloft over a number of nonurban areas of the United States tend to accumulate NOX emissions from the tall stacks of large fossil fuel power plants located at nonurban sites. During the night into the morning hours, the air aloft is isolated from any fresh NMOC emissions predominately coming from near surface sources. Conversely, during this extended period of restricted vertical mixing, air near the surface accumulates NMOC emissions while this air is isolated from the major NOX sources emitting aloft. These differences in the distribution of NMOC and NOX sources appear to account for the much larger NMOC to NOX ratios reported near ground level compared to aloft over nonurban areas.Two types of experimental results are consistent with these conclusions: (1) observed increases in surface rural NOX concentrations during the morning hours during which the mixing depth increases to reach the altitude at which NOX from the stacks of fossil fuel power plants is being transported downwind; (2) high correlations of total nitrate at rural locations with Se, which is a tracer for coal-fired power plant NOX emissions.The implications of these conclusions from the standpoint of air quality strategies are suggested by use of appropriate scenarios applied to both urban and regional scale photochemical air quality models. The predictions from urban model scenarios with NMOC to NOX ratios up to 20 are that NOX control will result in the need for the control of more NMOC emissions than necessary in the absence of NOX control, in order to meet the O3 standard. On a regional scale, control of NOX emissions from fossil fuel power plants has little overall effect regionally but does result on a more local scale in both small decreases and increases in O3 concentrations compared to the baseline scenario without NOX control. The regional modeling results obtained to date suggest that NOX control may be effective in reducing O3 concentrations only for a very limited set of conditions in rural areas.
Aerial ozone measurements were obtained during the summer of 1975 in the Northeastern United States. This paper reports on the results of a series of tests conducted upwind and downwind of several major metropolitan and industrial complexes, which include Phila-delphia-Camden-Wilmington and New York City-Northeastern New Jersey-Southeastern Connecticut. Flight patterns consisted of upwind and downwind tranverses perpendicular to the urban plume and vertical profiles. The results indicate significant O3 generation occurs in the urban plumes, but at no time was the difference between the upwind and downwind O3 concentrations greater than 0.08 ppm (maximum 0.078 ppm). However, in several cases when the upwind values were added to the O3 produced by the urban area, this was sufficient to result in violations of the NAAQS downwind. The paper also discusses the results of flights over refineries and petrochemical facilities which yielded a positive contribution to downwind O3 values.
Article
Twenty different chemical mechanisms used in studies of the formation of photochemical oxidants have been compared. In order to concentrate on the differences in the hydrocarbon chemistry, these mechanisms were modified so that each contained the same inorganic processes and so that the rate coefficients for the hydrocarbon degradation reactions were the same in most cases. The mechanisms were all implemented in a model to study the formation of photochemical oxidants downwind of London during midsummer, clear-sky, anticyclonic conditions. The same emissions inventory and meteorological parameters were used in each case. The mechanisms published since 1984 all produced similar results for ozone and nitric acid. The standard deviations of these concentrations were some 2–3 times greater when the whole set of results was considered. The concentrations of hydrogen peroxide and peroxyacylnitrates were much more variable, with concentrations varying by up to a factor of 2 for the recent mechanisms and with effectively no agreement over the whole set. This suggests that for these species, any agreement between observations and calculations which is within a factor of 2 is as good as can be expected and that model calculations cannot be verified to a greater degree of accuracy. The representation of hydrocarbon emissions in photochemical models and the ways in which large numbers of known atmospheric species are represented by a limited number of model variables clearly require further attention before confidence can be claimed in the model results for a wide range of photochemically generated secondary pollutants.
Article
The impact of nonmethane hydrocarbons of natural and anthropogenic origin on the photochemistry of the nonurban lower atmosphere has been studied using a photochemical model with detailed planetary boundary layer transport. The research was undertaken to evaluate the increase in peroxy radical concentrations due to hydrocarbon oxidation and their contribution to observed imbalances in the NO(x), O3 photostationary state. The results show that these hydrocarbons, at concentrations observed in the atmosphere, reduce the hydroxyl radical concentration in clean air and increase the peroxy radical concentration to levels that are needed to explain the observed imbalance in the photostationary state. For the conditions simulated here, natural hydrocarbons are the principal contributors to the increase in the peroxy radical concentration at low NO(x) mixing ratios. At higher NO(x) levels the anthropogenic hydrocarbons that scale with NO(x) gain in importance. Model simulations that include the hydrocarbons reproduce the observed dependence of the concentration of ozone on various NO(x) concentrations.
Article
In a coniferous forest area northeast of Oslo, Norway, air samples were collected by adsorption on activated carbon and analyzed by gas chromatography with a high resolution glass capillary column and flame ionization detection. During June and August 1980, seven terpenes were identified with a total concentration range of 8.8–70.7 ppbC (parts per billion, as carbon). α-Pinene, terpinene, and p-cymene occurred in the highest concentrations. A one-dimensional vertical grid model of the atmospheric boundary layer with a detailed mechanism for inorganic and organic gas phase chemical turnover was applied to assess the vertical variability of the terpene concentrations as a function of the ozone concentration, the source strength of the terpenes, the time of the day, the upwind air composition, etc. The calculations showed that very little of the terpene emissions remained airborne after 4–8 hours, in contrast to the anthropogenic hydrocarbons. It was found that the anthropogenic fraction of the hydrocarbons may dominate in concentration, even though the natural part of the source is the larger one. Emission of 2000 μg(m2 h)−1 of terpenes was calculated to give ground level concentrations of total terpenes of up to about 25 ppbC, comparable to or less than the measured concentrations. Terpene emission at this rate was shown to suppress the hydroxyl concentration compared to a model case with zero terpene emissions, while the impact on ozone during daytime was negligible.
Article
Measurements of natural hydrocarbon emission fluxes are reported for a northeastern U.S. deciduous forest, for a northwestern U.S. coniferous forest, and for dominant tree species in the Atlanta, Georgia, region. The emission data were obtained by using a vegetation enclosure procedure and a micrometerologial gradient technique. Isoprene fluxes determined by the gradient method in the deciduous forest varied from 2500 mug/m2/h at 20°C to 8000 mug/m2/h at 30°C. Corresponding fluxes obtained with the vegetation enclosure method ranged from 890 to 7300 mum/m2/h. Isoprene fluxes determined by both methods increased exponentially with increasing temperature. Emission rates from isoprene-emitting trees in the Atlanta area were similar to those observed in Pennsylvania. Alpha-pinene fluxes measured in a Douglas fir (Pseudotsuga menziesii) forest ranged from 9 to 1320 mug/m2/h. Relative humidity appeared to directly influence the alpha-pinene emission rate. The reasonable agreement between hydrocarbon fluxes obtained with two independent techniqus is significant evidence of the general validity of current biogenic hydrocarbon emission rates.
Article
Measurements of atmospheric monoterpene hydrocarbons were made at a site in the Colorado mountains. The research was undertaken to examine the influence of the compounds on the photochemistry of the troposphere. A sampling technique was developed using Tenax GC porous polymer traps with analysis by capillary gas chromatography and detection by flame ionization and mass spectrometry. Positive identification of six monoterpene hydrocarbons, -pinene, camphene, ]-pinene, myrcene, A-3carene, and d-limonene, was obtained, as well as tentative identification of -thujene and ]-phellandrene. A definite seasonal trend was evident in the average monoterpene mixing ratios. The summertime average was 0.30 ppbv for the sum of the five major identified monoterpenes, ]-pinene, -pinene, A-3carene, camphene, and d-limonene, with a high degree of constancy in relative ratios of each throughout the summer months. Wintertime measurements gave mixing ratios below the detection limits (0.001 ppbv of an individual compound). Simultaneous measurements of ozone, NO, NO2, and monoterpene hydrocarbons allowed examination of the contribution of monoterpene photooxidation to ozone production. Based on reported modeling studies, monoterpenes were estimated to be a small source of ozone, insufficient to account for the relatively high ozone mixing ratios (> 80 ppbv) sometimes observed at this sampling site.
Article
A gas-phase chemical kinetic scheme combined with a simple dispersion model has been used to examine the influence of season, time of release, and dispersion rate on the chemical behaviour of a power-plant plume emitted into an ambient atmosphere defined by urban emissions. Simulations were carried out over 24 h for a plume trajectory primarily over the sea at a typical Northern European latitude.The temporal behaviour of in-plume OH radical concentrations is a complex function of the parameters studied. For daytime releases, mean OH concentrations over 24 h are predicted to be lower than the ambient values. For evening and night releases, mean OH concentrations are calculated to be greater than the corresponding ambient values for rapidly dispersing plumes.Mean effective first-order rate constants for the gas-phase oxidation of plume SO2 are estimated to be ca 0.4% h−1, 0.2% h−1 and 0.02% h−1, for summer, autumn/spring, and winter, respectively, and are lower than the mean values calculated for the ambient troposphere.Ozone, H2O2 and PAN concentrations in power plant plumes are normally predicted to be less than the corresponding ambient values over most of the simulation period. A significant ozone excess in plumes is only expected for slowly dispersing plumes under summer conditions after 24 h.Most of the plume and ambient NOx is predicted to be converted to HNO3 in summer and autumn/spring within 24 h and concentrations of HNO3 are predicted to greatly exceed those of H2SO4.These results are compared with those obtained previously for simulations of dispersion into a ‘rural’ ambient atmosphere.
Article
The concentrations of O3, CO, dimethyl sulfide (DMS) and light hydrocarbons (C2–C4) were measured from an instrumented aircraft during February–April 1985, near the U.S. East Coast and in the vicinity of Bermuda as part of the Western Atlantic Ocean Experiment (WATOX). Sampling flights were performed within the boundary layer (BL) and in the free troposphere (FT) at both locations. Photochemical generation of O3 in polluted air parcels transported from the continent within the BL was identified as the probable source of excess O3 (up to 50 ppbv above background). Convective lifting of boundary layer air carried pollutants into the free troposphere. The concentrations of HC compounds in air sampled near Bermuda had a significant inverse relation to air mass transport time from the continent. The BL concentrations of the more reactive HCs (ethylene, propane, propylene, normal- and isobutane) declined faster than the less reactive HCs (acetylene and ethane), and were found to be proportional to air mass transport time over the ocean. DMS was detected, with few exceptions, only within the BL at both sampling locations. The average concentrations in the BL samples collected near the U.S. East Coast and in the vicinity of Bermuda were 27 and 54 pptv. In all samples taken in the BL the DMS concentration decreased sharply as a function of altitude.
Article
The O3 measurements from the Regional Air Monitoring System (RAMS) in St. Louis in the upwind and downwind flow directions have been used to evaluate the first day impact of the urban plume of St. Louis. The time periods between April and October 1975 and 1976 have been utilized for this purpose. Ozone formation in the urban plume has been evaluated with respect to the distribution of O3 concentrations at RAMS stations downwind. The relationships between O3 concentrations in the urban plume and such meteorological parameters as wind direction, wind speed, temperature, solar radiation intensity and maximum mixing heights have been investigated. Plume widths also have been estimated and related to plume O3 intensities.Incremental O3 formation within the urban plume compared to regional O3 background increases both in frequency and intensity from spring into midsummer and declines again in late summer and early fall. Episodic periods with substantial increments of O3 formation in the plume over background occur especially during the summer months. Aircraft measurements of O3 in the St. Louis plume are discussed by considering first day transport distances, plume widths and O3 profiles beyond the outer stations in the RAMS network.The significance of incremental O3 formation is evaluated in the St. Louis plume on population exposures as well as on fumigations of field crops or forest in rural areas downwind. The strongest effects of O3 formation in the plume occur in the prevailing wind direction. The O3 in the plumes from all of the cities in an interior region of the U.S. is estimated to impact 5–10% of the rural lands in this region on any given day.
Article
Emission rate vs temperature algorithms for different vegetation types, including deciduous, coniferous and agricultural sources, were used with available biomass and land use data for the U.S. to develop a national emission inventory with county spatial and monthly temporal scales. The estimated total NMHC emission rate from the U.S. is 30.7 Mt annually; more than half of these emissions occur in the summer, and approximately half arise in the SE and SW U.S. Total emission rates of isoprene from deciduous forest and α-pinene from deciduous and coniferous forests are 4.9 and 6.6 Mt annually. Emissions from agricultural crops contribute less than 3 % of the annual total. The average flux of biogenic NMHC in the U.S. is estimated to be 450 μgm−2h−1which is 20 times less than reported emissions of anthropogenic NMHC averaged over urban land areas in the U.S. Geochemical NMHC emissions from hydrocarbon rich soils in the U.S. are estimated to be negligible compared to vegetative sources. The uncertainty in the inventory is estimated to be on the order of a factor of three.
Article
The effects of dispersion into a range of ambient air conditions on the gas phase chemistry of typical power plant gaseous effluent mixtures have been modelled with particular reference to the formation of acidic products. A comprehensive chemical kinetic scheme coupled with a simple dispersion model has been adopted and calculations carried out for a range of dispersion rates and ambient air compositions under constant photolytic conditions.For the extreme conditions under which no mixing with ambient air occurs, the production of acidic pollutants is confined to the attack of oxygen atoms on SO2. In diluting systems, little conversion to acidic species can be ascribed to effluent materials expanding into a pure atmosphere or into ambient air containing no organic species. For expansion into air containing various levels of oxidant precursors and organic compounds, the major pathways for acid production are attack by OH radicals on SO2 and NO2. Peroxy radical attack on SO2 may also be important at longer times. Net conversions to sulphur and nitrogen acidic species attributable to effluent constitutents and their resulting concentrations are complex functions of dispersion rate and ambient air quality. In a real dispersing plume situation, interactions with ambient air will be even more complex and simple universal terms to account for plume chemsitry particularly in the near and medium field, are unlikely to be applicable.
Article
The literature on sources, emission rates, emission inventories, ambient air concentrations, lifetimes and reaction products of natural volatile organic compounds has been reviewed. Relationships between emission inventories and air quality measurements are considered. The effectiveness of natural hydrocarbons in contributing to ozone formation and aerosol formation in ambient air are discussed. It is concluded that natural hydrocarbons do not contribute substantially to the formation of either ozone or aerosols in ambient air.
Article
A photochemical model has been developed to determine the impact of the emission of light and terpenic hydrocarbons (HCs) on the evolution of ozone, HNO3 and PAN concentrations in the troposphere.The present model, of Lagrangian type, describes the evolution of trace gases in an air mass moving over a large and homogeneous source area. The respective cycles of O3, NOx, methane and CO are considered. The vertical exchange is treated by introduction of a vertical diffusivity tensor Kz varying as a function of time and altitude.The results of this study indicate that both the intensity of vertical exchanges of airborne elements and the ground deposition play an important role on the evolution of vertical concentration profiles. The influence of diffusivity on the integrated concentrations in the boundary layer remains low.The introduction of light HCs (alkanes, alkenes) results in an increase in the O3 concentration, correlated with the intensity of NOx and HC emissions. For a given level of NOx, both a decrease of the concentration in HNO3 and an increase in the PAN concentration are observable when the production of light HCs increases. The sensitivity increases with the NOx source.The introduction of terpenic HCs causes a depletion of O3 in the air masses characterized by low NOx emission rates, and an enrichment in those with higher emission rates. In both cases, the amplitude of the variation increases with the importance of the source of terpenic HCs, and is found higher for α-pinene than for isoprene.For a given NOx emission rate, the HNO3 concentrations are seen to decrease when the source of natural HCs increase, whereas the concentration in PAN increases. As observed for light HCs, the sensitivity shows a dependence on the magnitude of the NOx source.
Article
Data from a network of 20 ground-level O3 monitoring sites and two mobile remote sensing lidars have been used to quantify the formation of O3 in the London plume during 10 episodes between 1982 and 1986. Clear evidence is found of substantial O3 generation on a number of occasions, 9 days showing an enhancement of over 40 ppb and 3 days of over 70 ppb.The influence of the urban area on downwind O3 levels ranged from −18 to 72 ppb. The magnitude of the effect is found to correlate with the hours of sunshine, the maximum temperature, the regional daily 7-h average O3 level, the time of travel to the downwind site and inversely with wind speed. There was no apparent direct influence of wind direction. The ‘London effect’ on downwind O3 was seen in both the daily 1-h maximum and the daily 7-h average O3 concentrations, between which there is a high correlation.
Article
Sulfur hexafluoride tracer was used in a series of experiments to simulate isoprene emissions from an isolated oak grove. The measured tracer release rate and ambient concentrations of isoprene and SF6 observed along downwind sample lines were combined to determine the mass flux of isoprene from the forest. The fluxes determined from the tracer data increased exponentially with temperature and were in close agreement with estimates determined from emission rates measured in a series of branch enclosure samples. The results of this field study demonstrate the feasibility and usefulness of simulating forest emissions as a tool for investigating turbulent transport in forested areas. Isoprene emission fluxes that can be applied in regional models are reported.
Article
Concentrations of NO/sub 2/ in excess of the frequently quoted exposure limit of 190-320 ..mu..g of NO/sub 2//m/sup 3/ (95-160 ppb) as hourly mean have repeatedly been recorded in a street in Oslo during the winter. In Jan 1981, the hourly mean concentrations exceeded 200 ppb on 7 days; the maximum was 270 ppb. Summertime concentrations were much lower. with a simple model of the combined effects ofchemistry and dilution of the exhaust gas plume, it was shown that NO/sub 2/ generation through the reaction NO + NO + 0/sub 2/ ..-->.. NO/sub 2/ + NO/sub 2/ may explain a small fraction of the NO/sub 2/ formation. The study indicated that typically 5-10% of street level NO/sub x/ can be taken as NO/sub 2/ formed through this reaction. To account for the NO/sub 2/ measured, it is suggested that the NO/sub 2/ fraction of NO/sub x/ in car exhaust may be higher in the driving conditions found in Oslo during the winter than what is recorded in the standard cycles for car exhaust emissions testing.
Article
The results of modelling studies are reported together with a further analysis of an existing field measurement dataset. Emphasis is on the maximum ozone concentrations occurring in the urban plume from London, UK, on days of photochemical activity. Nitrogen oxide and volatile organic compound emissions from automotive exhausts are expected to be a large proportion of the total emission of these species, and the effect of their distinct diurnal variation is apparent in the field data. Factorial sensitivity studies on an expanding box model of the urban plume also show the dominance of urban emissions in the determination of plume maxima 100km downwind of the upwind urban boundary. These effects are not additive and depend strongly on the level of other variables.
Article
The effects of natural hydrocarbons must be considered in order to develop a reliable plan for reducing ozone in the urban atmosphere. Trees can emit significant quantities of hydrocarbons to metropolitan areas such as Atlanta, and model calculations indicate that these natural emissions can significantly affect urban ozone levels. By neglecting these compounds, previous investigators may have overestimated the effectiveness of an ozone abatement strategy based on reducing anthropogenic hydrocarbons.
Article
Isoprene emission rates from quaking aspen (Populus tremuloides Michx.) leaves were measured simultaneously with photosynthesis rate, stomatal conductance, and intercellular CO(2) partial pressure. Isoprene emission required the presence of CO(2) or O(2), but not both. The light response of isoprene emission rate paralleled that of photosynthesis. Isoprene emission was inhibited by decreasing ambient O(2) from 21% to 2%, only when there was oxygen insensitive photosynthesis. Mannose (10 millimolar) fed through cut stems resulted in strong inhibition of isoprene emission rate and is interpreted as evidence that isoprene biosynthesis requires either the export of triose phosphates from the chloroplast, or the continued synthesis of ATP. Light response experiments suggest that photosynthetically generated reductant or ATP is required for isoprene biosynthesis. Isoprene biosynthesis and emission are not directly linked to glycolate production through photorespiration, contrary to previous reports. Isoprene emission rate was inhibited by above-ambient CO(2) partial pressures (640 microbar outside and 425 microbar inside the leaf). The inhibition was not due to stomatal closure. This was established by varying ambient humidity at normal and elevated CO(2) partial pressures to measure isoprene emission rates over a range of stomatal conductances. Isoprene emission rates were inhibited at elevated CO(2) despite no change in stomatal conductance. Addition of abscisic acid to the transpiration stream dramatically inhibited stomatal conductance and photosynthesis rate, with a slight increase in isoprene emission rate. Thus, isoprene emission is independent of stomatal conductance, and may occur through the cuticle. Temperature had an influence on isoprene emission rate, with the Q(10) being 1.8 to 2.4 between 35 and 45 degrees C. At these high temperatures the amount of carbon lost through isoprene emission was between 2.5 and 8% of that assimilated through photosynthesis. This represents a significant carbon cost that should be taken into account in determining midsummer carbon budgets for plants that are isoprene emitters.
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